The present invention relates generally to wireless communication devices and more specifically to a method and apparatus for causing a wireless communication device to release semi-persistent uplink and/or downlink communication resources.
As used herein, the terms “user agent” and “UA” can refer to wireless devices such as mobile telephones, personal digital assistants, handheld or laptop computers, and similar devices that have telecommunications capabilities. In some embodiments, a UA may refer to a mobile, wireless device. The term “UA” may also refer to devices that have similar capabilities but that are not transportable, such as desktop computers, set-top boxes, or network nodes.
In traditional wireless telecommunications systems, transmission equipment in a base station or access device transmits signals throughout a geographical region known as a cell. As technology has evolved, more advanced equipment has been introduced that can provide services that were not possible previously. This advanced equipment might include, for example, an E-UTRAN (evolved universal terrestrial radio access network) node B (eNB), a base station or other systems and devices that are more highly evolved than the equivalent equipment in a traditional wireless telecommunications system. Such advanced or next generation equipment may be referred to herein as long-term evolution (LTE) equipment, and a packet-based network that uses such equipment can be referred to as an evolved packet system (EPS). As used herein, the term “access device” will refer to any component, such as a traditional base station or an LTE eNB (Evolved Node B), that can provide a UA with access to other components in a telecommunications system.
In mobile communication systems such as the E-UTRAN, the access device provides radio accesses to one or more UAs. The access device comprises a packet scheduler for allocating uplink and downlink data transmission resources among all the UAs communicating with the access device. The functions of the scheduler include, among others, dividing the available air interface capacity between the UAs, deciding the resources (e.g. sub-carrier frequencies and timing) to be used for each UA's packet data transmission, and monitoring packet allocation and system load. The scheduler allocates physical layer resources for downlink shared channel (PDSCH) and uplink shared channel (PUSCH) data transmissions, and sends scheduling information to the UAs through a physical downlink control channel (PDCCH). The UAs refer to the scheduling information for the timing, frequency, data block size, modulation and coding of uplink and downlink transmissions.
Several different data control information (DCI) message formats are used to communicate resource assignments to UAs including, among others, a DCI format 0 for specifying uplink resources and DCI formats 1, 1A, 2 and 2A for specifying downlink resources. Uplink specifying DCI format 0 includes several DCI fields, each of which includes information for specifying a different aspect of allocated uplink resources. Exemplary DCI format 0 DCI fields include a transmit power control (TPC) field, a cyclic shift demodulation reference signal (DM-RS) field, a modulating coding scheme (MCS) and redundancy version field, a New Data Indicator (NDI) field, a resource block assignment field and a hopping flag field. The downlink specifying DCI formats 1, 1A, 2 and 2A each include several DCI fields that include information for specifying different aspects of allocated downlink resources. Exemplary DCI format 1, 1A, 2 and 2A DCI fields include a HARQ process number field, an MCS field, a New Data Indicator (NDI) field, a resource block assignment field and a redundancy version field. Each of the DCI formats 0, 1, 2, 1A and 2A includes additional fields for specifying allocated resources. The access device selects one of the downlink DCI formats for allocating resources to a UA as a function of several factors including UA and access device capabilities, the amount of data a UA has to transmit, the amount of communication traffic within a cell, etc.
After a DCI formatted massage is generated, an access device may generate a cyclic redundancy check (CRC) for the message and append the CRC to the DCI formatted message. Next, the access device may use a Cell-Radio Network Terminal Identifier (C-RNTI) or Semi-Persistent Scheduling Radio Network Terminal Identifier (SPS-RNTI) that is uniquely associated with a UA to scramble the CRC prior to transmitting the message to the UA. When the message is received at the UA, the UA calculates the CRC from the received message, uses the C-RNTI or SPS-RNTI to scramble the CRC and uses the scrambled CRC to ascertain if the message was received accurately. If the CRC check indicates that the message was not intended for the UA (i.e. the CRC derived at the UA does not match to the CRC attached to the received message), the UA ignores the message.
Whenever control information has to be transmitted between an access device and a UA, the resources required to complete that transmission cannot be used to transmit other information such as voice or application information. For this reason the communications industry is always searching for ways to reduce the amount of control data required for controlling communications.
Two general types communication scheduling include persistent and semi-persistent. In persistent scheduling, as the label implies, communication resources are pre-allocated for a specific UA until released regardless of whether or not the resources remain in use during an entire scheduled period. For simple persistent scheduling this means that persistently scheduled resources are not available to other UAs for communication even when a UA that the persistent resource is assigned to is not using the resource.
In semi-persistent scheduling, a resource is assigned to a UA and is used on an on-going basis until the access device decides to stop using the resource and instructs the UA to stop using the resource. Thus, for instance, in the case of Voice over Internet Protocol (VoIP), a typical communication sequence may include interleaved “talk spurt states” and “silence states” where data corresponding to a UA user's speech is communicated during talk spurt states and no data except comfort noise information is communicated during silence states. During times of UA inactivity (e.g., silence states), the allocated uplink and downlink resources associated with a UA may be released so that the resources can be allocated to other UAs. Here, the uplink and downlink resources are persistently allocated in the sense that the resources remain allocated at long as the resources are being actively used to communicate information. Once resource use ceases, the resources are released. After resources are released, when a next talk spurt is to occur, the access device transmits one or more additional DCI formatted messages to the UA to commence a new SPS resource allocation to support the next spurt. Hereafter the phrase “SPS resources” will be used to refer to resources that are semi-persistently scheduled. In order to control SPS resource assignment, SPS-RNTI is used.
In the case of SPS resources, the communication industry has settled on ways to reliably activate and reconfigure SPS resources. Unfortunately, the industry has not developed a reliable way to cause a UA to release SPS resources.